This invention relates generally to fuel cell structures and is particularly directed to a modular structure for use in a matrix array of solid oxide fuel cells.
There are several types of fuel cells currently being studied as possible alternatives for converting coal derived fuels to electricity. The three primary types of fuel cells under study are the phosphoric acid (PAFC), molten carbonate (MCFC), and solid oxide fuel cell (SOFC). The most important single factor in assessing the viability of an alternative power generating concept is its overall capital and operational cost to the user compared to the cost of conventional power generating systems. A number of factors affecting the economics of power generation based upon the fuel cell need to be considered in evaluating the commercial viability of a given fuel cell approach. One of the primary factors to be considered is the capital cost of the power generating unit of the system. The present invention is directed to a low cost SOFC matrix and modules.
The modular SOFC system is considered to be one of the viable technologies for future commercial installations. In its simplest form, an SOFC modular system is comprised of an array of ceramic based fuel cell tubes connected in series and further includes parallel configurations having the necessary fuel and air manifolds, plenum exhaust outlets, electrical interconnects, etc. All such fuel cells further include cathode, electrolyte and anode layers which are deposited upon a porous support tube with an interconnecting strip to form series and parallel electrical connections.
Such cells or stacks of cells operate at high temperatures to directly convert chemical energy of a fuel into direct current electrical energy by electrochemical combustion. This type of fuel cell utilizes a natural or synthetic fuel gas such as those containing hydrogen, carbon monoxide, methane and an oxidant such as oxygen or air. A typical SOFC reacts hydrogen fuel with oxygen from air to produce electrical energy, water vapor and heat. Cell operating temperatures are typically in the range of from 700.TM. to 1100.TM.C. Each cell contains an electrolyte in solid form which serves to insulate the cathode and anode from one another with respect to electron flow, but permits oxygen ions to flow from the cathode to the anode. The hydrogen reaction on the anode with oxide ions generates water with the release of electrons; and the oxygen reaction on the cathode with the electrons effectively forms the oxide ions. Electrons flow from the anode through an appropriate external load to the cathode, and the circuit is closed internally by the transport of oxide ions through the electrolyte.
However, even the modular SOFC system presents a substantial challenge to the fuel cell designer in developing a commercially feasible fuel cell. For example, prior art SOFC approaches have required complicated cell support arrangements which make use of many interconnected components. In addition, the manner in which the individual cells are electrically coupled together as well as to a power output line has also resulted in overly complicated electrical connections. In addition to the aforementioned support and electrical coupling complexities, SOFC installations also must accommodate the fuel and oxidant gas inlet lines as well as an exhaust arrangement for discharging the burnt gases. These three considerations have complicated fuel cell design and substantially increased fuel cell costs. The present invention addresses the aforementioned limitations of prior art SOFCs by providing a fuel cell arrangement which is easily fabricated and assembled, makes use of low cost components, employs an integrated and common manifolding, bussing and structural support construction which allows for a substantial reduction in the cost of such fuel cells and greatly enhances their commercial feasibility.